A Combined 60/170 GHz Notch Filter for Collective Thomson Scattering at ITER

A Collective Thomson Scattering (CTS) diagnostic system is planned for the International Thermonuclear Experimental Reactor (ITER), which will be a primary diagnostic for measuring the dynamics of the confined fusion born alpha particles in the ITER plasma. The probe beam for this diagnostic comes from a 60 GHz 1 MW gyrotron. Since the measured signal close to the frequency of the probing beam is in the nW range, the receiver has to be protected with a narrow notch filter rejecting the gyrotron frequency. At the same time it also needs protection against stray radiation from the 20 MW ITER Electron Cyclotron Heating System (ECH), operating at 170 GHz.